Going pro with commercial ExpressionEngine add-ons
I've recently worked with a number of my clients to pitch the ExpressionEngine content management system -- it's by far my favorite, and it has earned a great reputation that is spreading fast. One of my favorite things is its commercial, professional nature: like many products, putting it behind a small pay wall dramatically improves the quality of both the software and the development community that has grown around it.
The fact that EE is already a commercial product also opens the door for third-party developers to build high-quality add-ons -- and make some extra dough in the process, allowing them to offer better support and better software. Here's a list of my favorite commercial EE add-ons, which are the icing on the cake for the thousands of smaller open-source contributions that make the CMS great. There's a price tag on each, but they pay for themselves every time.
Structure
The Structure module allows you to build a simple, flexible site hierarchy, making it easy to share templates across multiple pages. It also makes the control panel editing process leaps and bounds easier for the client to understand: they just see a site map, click on the title of the page, and make any changes they desire. It's not perfect for every site or content type, but for a lot of sites, it makes content management a breeze.
Wygwam
Speaking of editing content, the Wygwam extension hooks EE users up with the best what-you-see-is-what-you-get editor I've encountered so far... and I do a lot of content editing. It integrates seamlessly with EE's upload directories, allows you to create as many different toolbar combos as you need, and works with FieldFrame Matrix, allowing you to create more complex custom fields and more flexible content.
User
For sites that need more complex user signup and management, the User module frees you to build custom templates for all your member-related forms. By default, a lot of these forms are stuck in the somewhat rigid default EE templates (in the 1.x versions, at least), so this really frees you up to build a member interface to your unique needs. Also check out Tag, Rating, Favorites and many more from the same developer, Solspace.
Playa
Perhaps the most sexily named of the EE add-ons, Playa adds some promiscuity to your ExpressionEngine content. Built by the same prolific developer as Wygwam and FF Matrix, it allows you to create robust relationships between your blogs and content types, complete with AJAX filters and search options to ensure that your clients can pinpoint just the right content on a larger site. Although I build a lot of sites that don't need this functionality, this plugin has been my salvation on more complex jobs.
There are tons more great add-ons out there, too. Check out the EE Forums and Devot-EE for a vast database of options -- or just Google "ExpressionEngine" + whatever you need to do. There's something out there for just about everything.
In other news, don't miss my first published extension, Control Panel Home Page Redirect. What are your favorite ExpressionEngine add-ons?

I'm excited to release my first ExpressionEngine extension, the Control Panel Home Page Redirect. I've always found the EE control panel home page largely useless and confusing for my clients, and usually the first thing in my instructions is sending them to a certain tab -- often the one for the 
